Television receiver with partially by-passed non-linear luminance signal processor

Abstract

A composite video input signal is separated into luminance and chrominance components by a signal separation filter and the components are applied to a display processor having a video display device coupled thereto for providing displayed images. For enhancement of detail in dark and light areas of the displayed images, the luminance signal is coupled to the display processor via a non-linear luminance signal processor which provides additional amplification in the dark and light areas but tends also to degrade the signal to noise ratio in those areas. To avoid a loss of signal to noise ratio in the enhanced areas the receiver includes a by-pass circuit for by-passing high frequency components of the luminance signal around the non-linear luminance signal processor and a filter in the non-linear luminance signal processor for attenuating the high frequency components.

What is claimed is: 
     
       1. A television receiver, comprising: a signal separation filter for separating a composite video input signal supplied thereto into a luminance component and a chrominance component;   a display processor having a chrominance signal input coupled to receive said chrominance component, having a luminance signal input coupled via a non-linear luminance signal processor to receive said luminance signal component and having an output coupled to a display device for displaying images having enhanced detail in luminance signal level ranges determined by said non-linear luminance signal processor,   said non-linear luminance signal processor being of a type having relatively increased gain within a predetermined amplitude range between black level and white level;   characterized in that   for reducing a tendency of said non-linear luminance signal processor to accentuate differences in displayed picture noise levels under relatively low input signal-to-noise ratio conditions, said receiver further comprises:   a signal summing circuit having an output coupled to said luminance signal input of said display processor and having first and second inputs;   a high-pass filter for coupling said luminance component to said first input of said signal summing circuit;   said non-linear luminance signal processor being coupled between an output of said signal separation filter and said second input of said signal summing circuit; and   a low-pass filter disposed in said non-linear luminance signal processor so that a processed luminance signal produced by said signal summing circuit is representative of a sum of a linearly processed high frequency component and a non-linearly processed low frequency component thereby reducing said tendency of said non-linear processor to accentuate said differences in said displayed picture noise levels under said relatively low input signal-to-noise ratio conditions.   
     
     
       2. A television receiver as recited in claim 1 wherein: said high pass filter has a given corner frequency; and   said low pass filter has a corner frequency substantially equal to said given corner frequency of said high pass filter.   
     
     
       3. A television receiver as recited in claim 2 wherein: said high pass filter further comprises peaking means coupled thereto for applying peaking to high frequency components of said luminance component coupled to said signal summing circuit by said high pass filter.   
     
     
       4. A television receiver, comprising: a signal separation filter for separating a composite video input signal supplied thereto into a luminance component and a chrominance component;   a display processor having a chrominance signal input coupled to receive said chrominance component, having a luminance signal input coupled via a non-linear luminance signal processor to receive said luminance signal component and having an output coupled to a display device for displaying images having enhanced detail in luminance signal level ranges determined by said non-linear luminance signal processor;   first circuit means connected in parallel with said non-linear luminance signal processor for by-passing high frequency components of said luminance component around said non-linear luminance signal processor;   second circuit means in said non-linear luminance signal processor for attenuating high frequency components of said luminance component processed by said non-linear luminance signal processor;   said first circuit means comprising a high pass filter having a given corner frequency;   said second circuit means comprising a low pass filter having a corner frequency substantially equal to said given corner frequency; and wherein:   said non-linear luminance signal processor comprises first and second non-linear processors coupled in cascade by a buffer amplifier, said first non-linear processor having a predetermined load impedance and said second circuit means comprises a capacitor coupled between said load impedance and a source of reference potential.